Age-related changes in the cerebellum such as Purkinje cell loss and accumulation of neuronal lipofuscin are found to occur both in rats and man. This project proposes to investigate the morphology of aging neurons in the cerebellar cortex of the Fisher 344 rat with the Rapid Golgi method. Camera lucida drawings and photographs will be made at the light microscopic level of the cell bodies, dendritic arbors and local axon plexes of Purkinje cells, granule cells, Lugaro cells, Golgi cells, stellate cells, basket cells and the local projections of mossy fibers and climbing fibers. Measures will be made of dendritic length and spine density at selected dendritic sites.